Dipole ion source

ABSTRACT

A dipole ion source (FIG.  1 ) includes two cathode surfaces, a substrate ( 1 ) and a pole ( 3 ); wherein a gap is defined between the substrate and the pole; an unsymmetrical mirror magnetic field including a compressed end, wherein the substrate is positioned in the less compressed end of the magnetic field; and an anode ( 4 ) creating an electric field penetrating the magnetic field and confining electrons in a continuous Hall current loop, wherein the unsymmetrical magnetic field serves an ion beam on the substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present patent application claims the benefit of the filingdate of U.S. provisional patent applications Serial Nos. 60/285,360;60/285,361; and 60/285,364, each of which was filed on Apr. 20, 2001 andeach of which is hereby incorporated by reference.

[0002] This application also incorporates by reference PCT applicationsserial Nos. ______ (attorney docket no. 10630/14) and ______ (attorneydocket no. 10630/15), both of which designate the U.S. and are beingfiled on the same date as the present application.

BACKGROUND

[0003] The present invention relates to a dipole ion source. Beforeturning to the detailed description of the presently preferredembodiments, related prior art is discussed below. The related prior artis grouped into the following sections: extended acceleration channelion sources, anode layer ion sources, Kaufman type ion sources, Penningdischarge type ion sources, facing target sputtering, plasma treatmentwith a web on a drum, and other prior art methods and apparatuses.

[0004] Extended Acceleration Channel Ion Sources

[0005] Extended acceleration channel ion sources have been used as spacethrust engines and for industrial ion sources for many years. Theembodiments described in U.S. Pat. No. 5,359,258 to Arkhipov et al. aretypical examples of these sources. These sources have a separateelectron source to provide electrons to the ion source. Pole erosion isan issue with these sources.

[0006] Anode Layer Ion Sources

[0007] Anode layer ion sources (see U.S. Pat. No. 5,838,120 to Semenkinet al.) are another variation of ion source that places the anode tointerrupt a portion of the electron containing magnetic field. Thesesources do not require a separate electron source. Recently, they havebeen commercialized for industrial use by Advanced Energy Industries,Inc. and other vendors. Similar to the extended acceleration channelsources, the substrate is placed outside the containing magnetic field,outside the gap between cathode surfaces.

[0008] Kaufman Type Ion Sources

[0009] Kaufman, working at NASA, developed this type of ion source to ahigh level in the early 1960's (see J. Reece Roth, Industrial PlasmaEngineering, Volume 1: Principles, pp200-204, IOP Publishing, Ltd.1995). These sources place the substrate outside of the electronconfining magnetic field.

[0010] Penning Discharge Type Ion Sources

[0011] Several variations of a Penning discharge type ion source arediscussed in J. Reece Roth, Industrial Plasma Engineering, Volume 1:Principles, pp 204-208 and FIG. 9.31, IOP Publishing, Ltd. 1995.

[0012] Facing Target Sputtering

[0013] U.S. Pat. No. 4,963,524 to Yamazaki shows a method of producingsuperconducting material. An opposed target arrangement is used with thesubstrate positioned between the electrodes in the magnetic field. Inthis method, the magnetic field is symmetrical between the electrodesand the substrates are in the middle of the gap. When the substrates areplaced in this position, the tall current generated within the magneticfield tends to be distorted and broken, and the plasma is extinguishedand/or the voltage is much higher.

[0014] Plasma Treatment with a Web on a Drum

[0015] In U.S. Pat. Nos. 5,224,441 and 5,364,665 to Felts et al., aflexible substrate is disposed around an electrified drum with magneticfield means opposite the drum behind grounded or floating shielding.Magnetic field lines are not shown.

[0016] In U.S. Pat. No. 4,863,756 to Hartig et al., the substrate iscontinuously moved over a sputter magnetron surface with the surfacefacing the magnetron located inside the dark space region of thecathode. In this way, the magnetic field of the magnetron passes throughthe substrate and is closed over the substrate surface constricting theplasma onto the surface.

[0017] Other Prior Art Methods and Apparatuses

[0018] In U.S. Pat. No. 4,631,106 to Nakazato et al., magnets arelocated under a wafer to create a magnetron type field parallel to thewafer. The magnets are moved to even out the process. The opposed plateis grounded, and the wafer platen is electrified. U.S. Pat. No.4,761,219 to Sasaki et al. shows a magnetic field passing through a gapwith the wafer on one electrode surface. U.S. Pat. No. 5,225,024 toHanley et al. has a mirror magnetic field where a cusp field isgenerated to create flux lines parallel to the wafer surface. In U.S.Pat. No. 5,437,725 to Schuster et al., a metal web is drawn over a drumcontaining magnets.

SUMMARY

[0019] The present invention is defined by the following claims, andnothing in this section should be taken as a limitation on those claims.

[0020] By way of introduction, the preferred embodiments described belowrelate to a dipole ion source. In one preferred embodiment, a dipole ionsource is provided comprising a substrate; a pole, wherein a gap isdefined between the substrate and the pole; an unsymmetrical mirrormagnetic field comprising a compressed end and a less compressed end,wherein the substrate is positioned in the less compressed end of themagnetic field; and an anode creating electric fields from both thesubstrate and pole surfaces that penetrate the magnetic field andconfine electrons in a continuous Hall current loop, wherein theunsymmetrical magnetic field serves to focus an ion beam on thesubstrate.

[0021] Other preferred embodiments are provided, and each of thepreferred embodiments can be used alone or in combination with oneanother. The preferred embodiments will now be described with referenceto the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 shows a section view of a dipole ion source apparatus of apreferred embodiment.

[0023]FIG. 2 shows an isometric view of the apparatus of FIG. 1.

[0024]FIG. 3 shows a section view of a dipole ion source for waferprocessing.

[0025]FIG. 4 shows a section view of a dipole ion source for treatingplanar substrates.

[0026]FIG. 5 shows a section view of a dipole ion source employing acentral magnet to return the field.

[0027]FIG. 6 shows a section view of an apparatus for treating flexibleweb substrates.

[0028]FIG. 7 shows a section view of another plasma apparatus fortreating flexible web substrates.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0029]FIG. 1 shows a section view of a dipole ion source. In this case,the substrate 1 is a high permeability, electrically conductive materialsuch as steel sheet. A magnetic field is set up in the gap between thesubstrate 1 and magnetic pole 3 with permanent magnet 2. Pole 3 iselectrically conductive and is connected to ground as is substrate 1.Pole 3 is water cooled through gun drilled hole 7. Anode 4 is watercooled with brazed on tubes 5 and is attached to support plate 6 withscrews 13. Magnet 2 is an electrical insulator. The anode and magnetassembly are supported over the substrate 1 with a bracket not shown.The fundamental operation of the dipole ion source takes advantage ofthe understanding that the electron Hall current can be contained withina simple dipole magnetic field rather than a racetrack shaped field.This effect has been used to produce other novel sources in thefollowing patent applications: PCT applications serial nos. ______(attorney docket no. 10630/14) and ______ (attorney docket no. 10630/15)and U.S. patent application Ser. No. 10/036,067, which is herebyincorporated by reference. This effect is used in a dipole ion source tocreate a simple, effective ion beam source with distinct advantages.

[0030] The dipole ion source power supply 14 in this case is a DC supplycapable of 4000VDC. The positive electrode is connected to anode 4, andthe return path is via the substrate 1 and pole 3 through ground. Asshown, the source will operate very similarly to an anode layer ionsource. At higher pressures, above ˜3 mTorr, the source operates in adiffuse or plasma mode. In this mode, a conductive plasma 9 fills themagnetic confined region as shown, and the electric fields shift to thesheaths at the grounded and anode surfaces. At lower pressures, theconductive plasma disappears, and a distinct plasma beam 10 can be seenemanating from anode layer region 8. Without the conductive plasma 9,the static electric fields 11 dictate the electron and ion flows. Thismode is termed the collimated mode. In the collimated mode, the voltageof the source is more directly proportional to power requiring thehigher voltage DC supply. In the diffuse mode, voltages in the 300-600volt range are typical.

[0031] The difference with prior art is that instead of using aracetrack magnetic field and separating the source from the substrate,the dipole magnetic field is shared between the source and substrate.There are several benefits to this arrangement:

[0032] Operation in the diffuse mode is particularly benefited. Inexisting grid less or anode layer ion sources, the diffuse mode presentsdifficulties. Firstly, the cathode poles tend to be sputter erodedcontaminating the substrate and requiring expensive maintenance.Secondly, the intense plasma region is separated from the substrate.This is because the source plasma remains inside the racetrack openingbetween the cathode surfaces. With the dipole ion source of thispreferred embodiment, the plasma is in direct contact with thesubstrate. As shown in FIG. 1, the substrate is a pole of the source.This allows a high degree of plasma interaction with the substrateincreasing processing rates.

[0033] Pole erosion by sputtering is greatly reduced in both the diffuseand collimated modes. Pole 3 erosion is reduced due to two designfactors. The magnetic mirror effect tends to push electrons and ionsaway from the pole reducing plasma contact. The unsymmetrical magneticfield focuses plasma ions-toward the substrate rather than the exposedpole. Also, the location of the anode close to pole 3 directionallypoints the ion flow toward the substrate. Additionally, because one ofthe two poles is the substrate, there is one less pole to erode.

[0034] Neutrality of the beam is assisted by the beam never leaving themagnetically confined region 12. This reduces glow around the chamberand particularly benefits PECVD operations where deposition occurswherever there is glow. In these processes, spurious glow causesdeposition in unwanted places causing process drift and additionalmaintenance.

[0035] The source is a simple, economic design. By confining theelectron Hall current in a simple dipole magnetic field, long sourcescovering wide substrates can be readily constructed. Complex racetrackmagnetic fields are not needed. The source of FIG. 1 can easily beextended to cover a 2 or 3 meter wide substrate.

[0036]FIG. 2 shows an isometric view of the source depicted in FIG. 1.This shows how the source can be extended to process wide substratewidths. At the end of the source, the anode 4 cover has been left off toshow the internal magnet 2 and pole 3. Water cooling tube 5 passesaround both sides of anode 4. The end plates of anode 4 are cooled byconduction through the anode material (such as copper) to the watercooled side regions. Plasma 9 is contained within electron magnetizingfield region 12. While magnetic fields are present around and behind theplasma source, electric fields are not present to light a plasma. Forsafety, a grounded shield is recommended around the entire source. Thisis not shown for clarity, and this form of shielding is well known inthe art.

[0037]FIG. 3 shows an implementation of the preferred embodiment forsemiconductor wafer processing. In this source, the wafer 21 is placedon platen 20. Platen 20 is made of a high permeability material. Anunsymmetrical magnetic mirror field is generated through the waferacross a gap with magnet 22, shunt 26, and magnets 24. The mirror fieldis designed to expand out from magnet 22 over wafer 21. Cover 23protects magnet 22 from the plasma and can be left either floating orcan be tied to power supply 34. Magnet 22 is an electrical insulator.When cover 23 is tied to power supply 34, the source takes the form of aPenning cell. This is a very efficient magnetic plasma containmentbottle. By connecting magnetic shunt 26 as the opposed electrode toplaten 20, the required electric field lines are created penetrating themagnetic field lines 32 to contain the Hall current within field 32.Magnet 22 is a bar magnet long enough to span the width of the wafer.When plasma 29 is lit, the Hall current is confined and creates a bar ofplasma 29 between the magnet cover 23 and wafer 21 along the length ofmagnet 22. Platen 20 is rotated to uniformly treat the wafer withplasma.

[0038] The uniqueness of this source has several components:

[0039] Highly energetic ion bombardment of the wafer is achieved with adense plasma over the wafer surface. Prior art implementing RF on thewafer and an opposed electrode (where 26 is located) without a magneticfield has a less dense plasma. Sources with a magnetic field connect theequivalent of cover 23 to the opposed electrode of the power supply.This decreases the degree of electron containment and decreases overallplasma density.

[0040] The Hall current containment within the dipole magnetic fieldproduces a line of uniform plasma over the full wafer surface. Byrotating or moving the magnet or wafer, uniform processing of the waferis possible.

[0041] The use of the mirror magnetic field at the magnet cover 23allows the cover to be electrically floating. This dramatically reducessputtering of cover 23. Contamination of the wafer with sputteredmaterial and wear of cover 23 is eliminated.

[0042] The showerhead shape of the magnetic field produces a directedflow of ions toward the wafer surface. This can be tailored to suit theapplication. By enlarging the gap between magnet 22 and platen 20, theshowerhead shape changes to an onion shape. This changes the focusingcurve of the magnetic field to redirect the ion flow into the center ofthe gap, and ion impingement on the wafer is reduced. The ability tocontrol the ion impingement rate and angle of impingement is a benefitof this preferred embodiment.

[0043]FIG. 4 shows a section view of a dipole ion source for processingplanar electrically insulating substrates such as glass. In this source,a window 95 constructed of non-magnetic, electrically conductive metalis positioned over the substrate. The magnetic field is created perthese preferred embodiments through the gap between the substrate 101and pole 94 by permanent magnets 96, 98 and 100 and shunts 97, 91, 92and 93. The use of a thin shunt 93 under the substrate causes themagnetic field 106 to bloom out, creating a wide showerhead field. Thecurving M field lines tend to focus ions like a satellite dish. With awide showerhead field as shown, the ions are directed toward thesubstrate. A racetrack electron Hall current confined region is createdbetween window 95 and pole 94 within the magnetic field lines that passbetween these surfaces. Tubular ring anode 102 is positioned tointerrupt a portion of the magnetic field lines passing between thewindow 95 and pole 94. This placement produces a version of the anodelayer effect of a typical anode layer source. The benefit of thisplacement is that enough electrons are generated by the sharp electricfield around the anode to produce a large ion flow even at pressuresbelow 1 mTorr. This can be seen in operation as a blue flame 105pointing toward the substrate. In an anode layer source, this is thetypical collimated mode of operation. When the pressure is raised, adense plasma 107 fills in the magnetically confined region between thewindow 95 and pole 94. Power supply 90 is connected between anode 102and cathodes C, the window 95, and pole 94. This power supply can beeither a DC power supply or an AC or RF supply. In the case of PECVD ofan insulating coating, the use of AC or RF can allow current to passthrough coating build-up on the electrode surfaces. Note that in thisarrangement, either the anode or the window and pole cathodes can begrounded with the opposed electrode at the required high or low,respectively, voltage.

[0044]FIG. 5 shows another version of the preferred embodiment. In thissource, the primary mirror field 8 is set up around the periphery of thereturn magnetic field 10. Magnets 4 and 5 and shunts 2 and 3 are used tocreate the magnetic fields as shown. Shunt 2 is positioned under thesubstrate and is connected as part of one electrode of power supply 7.Substrate 1 is a dielectric material such as a polymer web and powersupply 7 is an AC supply of sufficient frequency to pass current throughthe substrate 1. Cover 12 is electrically conductive and is connected toshunt 3 and power supply 7. Anode 6 circumvents the source as shown andis the opposed electrode to cover 12 and, effectively, substrate 1.Again, this source can be operated in either the collimated or diffusemodes. The anode 6 is shown in this view to be removed outside of themagnetic field lines 8 that pass through electrodes 12 and 2. Thissource will therefore operate less efficiently in the collimated modeand may require a separate source of electrons 17. Note that theelectrons must be inserted between the containing magnetic field 8 andthe anode for proper operation.

[0045] In this source arrangement, there is only minimal containment ofelectrons in the central magnetic field 10. This is because the electricfields 15 and 16 do not penetrate that far between the cover andsubstrate. This produces a “virtual cathode” between cover 12 andsubstrate 1 and causes an ion flow 11 toward the substrate. Duringoperation, a plasma ring 9 is readily visible.

[0046]FIG. 6 is a section view of a source employing a central returnmagnetic field. In this source a flexible web substrate 3 is supportedby rollers 1 and 2. Non-rotating “magnetron” magnet arrays 20 and 21create magnetic fields 13 and 22 as shown. Magnetic field 13 forms aracetrack endless loop around field 22. Anode electrode 12 circumventsroll 1 and is a water cooled tube. Rolls 1 and 2 are connected viabrushes (not shown) to power supply 23. Power supply 23 is an AC powersupply of sufficient frequency to pass current effectively throughdielectric substrate material 3. If the substrate is electricallyconductive, a DC power supply can be used. By positioning anode 12 closeto roll 1, the electric fields 15 and 19 tend to focus ions onto roll 2.The advantage of this source is that in a PECVD operation, activespecies formed in the plasma region are in proximity to the substraterather than source components. This increases the rate and efficiency ofthe coating process and reduces cleaning maintenance. While thisimplementation closely follows the continuously moving Penning cellwork, the concept of moving the anode to direct impinging ion flow isnot well covered in that application.

[0047]FIG. 7 shows a section view of another web plasma source. Thissource is designed to operate in the diffuse mode. Two rolls 201 and 202support web substrate 200. Roll 201 is a 400 series (magnetic) stainlesssteel roller. Roll 202 is constructed of non-magnetic stainless steel(300 series) and has magnets 206 and 208 and shunt 207 positioned insidethe roller. Magnets 206 and 208 and shunt 207 do not rotate with roller202. Rollers 201 and 202 are water cooled by known techniques.Unsymmetrical magnetic field 211 is created in the gap by the magnets inroller 202 and magnets 204 and shunt 203. Rolls 201 and 202 areconnected to one side of power supply 212 with shunt 205 and the chamberground as the opposed electrode. Shunt 205 also acts to collect straymagnetic field from the permanent magnet region. When power supply 212is turned on and with gas pressure of between 1 and 100 mTorr, a plasma210 lights between rollers 201 and 202. The conductive plasma 210created can be used to plasma coat, plasma treat or etch the websubstrate. Note that no Hall current ring is apparent in the diffusemode of operation as the bright plasma 210 overwhelms a visible Hallring. Several unique, useful sources can be created with variations onthis theme. For instance, roll 201 can be made of a non-magneticmaterial. While less magnetic field will pass across the gap into roll201, with strong magnets 206, 208, etc. sufficient field will be presentto confine a plasma per the inventive method. In another variationuseful with an insulating substrate 200, roller 202 (and subsequentlysubstrate 200) may be left floating or grounded. Switch 215 is shown forthe purpose of changing the electrical connection to roll 202. This canbe done if the magnetic mirror field at the surface of substrate 200 onroll 202 is strong enough (the magnetic field strength at the surface ofsubstrate 200 on roll 202 is greater than twice the strength of thefield in the gap along the same field line) to repel electrons andconfine the plasma. An example of usefulness is an existing coatingsystem with an electrified, non-magnetic drum could be modified to add afloating or grounded roll 202 as shown with magnets, etc. The magneticreturn path could be left off. With the substrate covering roll 202 perthe inventive method, the benefits of not coating plasma facingshielding and the substrate receiving the additional plasma coating areobtained. The lowering of maintenance and increasing deposition rate areimportant commercial improvements to known plasma processes. Additionalvariations and teachings are made in PCT applications serial nos. ______(attorney docket no. 10630/14) and ______ (attorney docket no.10630/15), both of which designate the U.S. and are being filed on thesame date as the present application.

[0048] It is intended that the foregoing detailed description beunderstood as an illustration of selected forms that the invention cantake and not as a definition of the invention. It is only the followingclaims, including all equivalents, that are intended to define the scopeof this invention.

What is claimed is:
 1. A dipole ion source comprising: a substrate; apole, wherein a gap is defined between the substrate and the pole; anunsymmetrical mirror magnetic field comprising a compressed end and aless compressed end, wherein the substrate is positioned in the lesscompressed end of the magnetic field, wherein the pole and the substrateare charged to contain electrons; and an anode positioned to create anelectric field penetrating the magnetic field and confining electrons ina continuous Hall current loop, wherein the unsymmetrical mirrormagnetic field serves to focus an ion beam on the substrate.
 4. Theinvention of claim 1, wherein the substrate is conductive and is biasedwith one of an AC or RF source.
 5. The invention of claim 1, wherein thesubstrate is insulating and is biased with one of an AC or RF source. 6.The invention of claim 1, wherein the substrate is conductive and isbiased with a DC source.
 7. The invention of claim 1, wherein thesubstrate is moved relative to the magnetic field.
 8. The invention ofclaim 1, wherein the magnetic field is moved relative to the substrate.9. The invention of claim 1, wherein the substrate comprises a flexibleweb supported by a conveyor roll.
 10. The invention of claim 9, whereinboth the conveyor roll and the pole are largely shielded from the plasmaby the substrate
 11. The invention of claim 1, wherein the substratecomprises a rigid wafer.
 12. The invention of claim 1, wherein themagnetic field is created by a permanent magnet.
 15. The invention ofclaim 1 or 16, wherein the invention further comprises an electronneutralization source.
 16. A dipole ion source comprising: a substrate,wherein the substrate is charged to contain electrons; a pole, wherein agap is defined between the substrate and the pole; an unsymmetricalmagnetic field comprising a compressed end and a less compressed end,wherein the substrate is positioned in the less compressed end of themagnetic field; further wherein at least a portion of the magnetic fieldadjacent to the pole is at least two times stronger near the pole thanadjacent to the substrate surface; and an anode positioned to create anelectric field penetrating the magnetic field and confining electrons ina continuous Hall current loop, wherein an ion beam is focused on thesubstrate; wherein the substrate is moved in relation to the magneticfield, thereby providing uniformity in treatment.
 17. The invention ofclaim 16, wherein the pole is negatively biased to confine electrons inrelation to the anode.
 18. The invention of claim 16, wherein the poleis electrically connected to the substrate potential.
 19. The inventionof claim 16, wherein the pole is electrically floating.
 20. Theinvention of claim 16, wherein the pole is biased at the anodepotential.
 21. The invention of claim 1, wherein the ion source operatesbelow 2 mTorr in a collimated mode.
 22. The invention of claim 1,wherein the ion source operates above 1 mTorr in a diffuse mode.
 23. Theinvention of claim 16 further comprising a magnetic field structure. 24.The invention of claim 23, wherein the magnetic field structurecomprises a high permeability member.
 25. The invention of claim 23,wherein the magnetic field structure comprises a magnet.
 26. Theinvention of claim 23, wherein the magnetic field structure is locatedbehind the substrate and the pole.
 27. The invention of claim 23,wherein the magnetic field structure is located behind the pole but notthe substrate.
 28. The invention of claim 16, wherein the pole iscovered by the substrate.
 29. The invention of claim 16, wherein thepole is biased at a different potential than either the substrate or theanode.
 30. The invention of claim 16, wherein at least a portion of themagnetic field adjacent to the pole is at least four times stronger nearthe pole than adjacent to the substrate surface.
 31. The invention ofclaim 16, wherein at least a portion of the magnetic field adjacent tothe pole is at least eight times stronger near the pole than adjacent tothe substrate surface.
 32. The invention of claim 1 or 16, wherein themagnetic field is concave in relation to the anode.
 33. The invention ofclaim 1 or 16, wherein the magnetic field is convex in relation to theanode.
 34. The invention of claim 1 or 16, wherein the anode ispositioned within a portion of the magnetic field to further assist withfocusing an ion bean onto the substrate.
 35. The invention of claim 1,wherein the substrate is moved in relation to the magnetic field,thereby providing uniformity of treatment.